Evaporators with a stationary heater or circulation evaporators are used for thickening liquid with solid contents. Circulation evaporators have a higher evaporating efficiency, but fail in the case of viscous products, or when there are higher solid concentrations in the liquid. Conventional film-type evaporators with fixed evaporating surfaces do not have an adequate evaporating efficiency, whereas those having rotating evaporating surfaces operate with very thin liquid films, which can no longer be maintained with larger solid particles. The particles do not flow along, the film breaks and there is local overheating, which in turn leads to caking and encrustations.
The problem of the present invention is to so construct an apparatus of the aforementioned construction, that a high evaporating efficiency is obtained and it is possible to thicken the liquid up to a relatively high solid content.
According to the invention this problem is solved in that the heater is constructed as a rotor rotating in the container and is formed from a plurality of substantially parallel plates arranged with a limited axial spacing and extending outwards from the rotor axis, every second space between adjacent plates forming a heating chamber sealed with respect to the liquid, while the spaces located between the same close to the rotor axis and on the circumference thereof are open towards the container interior.
Between the plates arranged with a limited axial spacing are formed axially symmetrical gaps, which alternately serve as a heating chamber and an evaporating chamber, in that the spaces located between the heating chambers and close to the rotor axis and externally are open to the liquid present in the container. As a result of the rotation of the rotor the liquid between the plates is centrifugally accelerated towards the outside, i.e. is constantly "sucked" from the inside and transported to the outside. As a result of the limited distance between adjacent heating surfaces, which define an evaporating chamber, high flow forces act on the liquid which, in conjunction with a correspondingly high speed, ensure a constant cleaning of the chamber, so that the solid particles cannot become attached to the heating surfaces. The rotor does not act solely as a heater, but also as a pump, the friction between the liquid and the plates bounding the heating chambers keeping the same clean. The heat carrier can be guided in the heating chambers in such a way that it is also transported from the inside to the outside as a result of the centrifugal forces.
According to an advantageous embodiment, the rotor has a lower part forming a heat carrier chamber and which in its center and on its circumference carries the plates joined together in a stack-like manner.
The present embodiments are in particular characterized by a simple construction, which is of a self-supporting nature for the rotor. The heat carrier for the heating chambers is supplied by means of the lower part. For example, the lower part can be connected by means of a hollow drive shaft of the rotor to a heat carrier circuit.
A simple construction is obtained if the plates close to the rotor axis and close to its circumference are interconnected and connected to the lower part by means of several symmetrically distributed screw bolts with spacers. Thus, the rotor can easily be adapted to the particular requirements (container volume, evaporating efficiency, etc.), in that a corresponding number of plates are combined in stack-like manner and fixed together by means of the screw bolts.
Another appropriate embodiment is characterized in that the heating chambers close to the rotor axis are connected by means of at least one axially parallel, hollow bolt to the heat carrier chamber in the lower part and on the circumference with at least one further axially parallel hollow bolt issuing into the lower part. Appropriately all the screw bolts form the hollow bolts for the supply and/or removal of the heat carrier.
If it is a vaporous heat carrier, then condensate is deposited on the external bolts and as a result of the rotating rotor the condensate collects at the outside and can be removed therefrom by a skimming tube.
In order to avoid a corotation of the liquid in the container as a result of the rotation of the rotor, above the rotor in the container and below the liquid level are provided flow-breaking fittings. These can be plates, strips or the like arranged crosswise within the container.
The plates bounding the heating chambers and the evaporating chambers can be arranged in radial planes with respect to the rotor axis. This leads to a particularly flat or shallow construction. However, in place of this, over at least part of their radial extension the plates can rise conically towards the outside. As a result, for the same radial extension, the flow paths in the evaporating chambers can be lengthened and the effective shear forces are further increased. This can be alternately or additionally achieved in that the plates are constructed as corrugated plates over at least part of their radial extension.
The invention is described in greater detail hereinafter relative to two non-limitative embodiments and the attached drawings: